Causes and control of cold-rolled steel surface black spot defects

Causes and control of cold-rolled steel pipe surface black spot defects

If the emulsion removal on strip surface is not clean, easy to form black spot defects after annealing, seriously affect the quality of the strip surface. There are for the following reasons:

1, chilled coil-shaped mass can significantly affect the annealing process emulsion volatile, such as strip existence waves, wave shape will be very detrimental to the volatile layers of emulsion.

2, the surface roughness of the strip, the larger the roughness, the coil layer and the interface layer, the gap increases, the volatile beneficial emulsion.

3, the winding tension of the rolling passes of the finished product, reducing the winding tension, to increase the gap between the layers, the protective gas flowing between the coil layer may be sufficiently volatile to ensure emulsion.

4, emulsion volatile, emulsions good thermal volatility can greatly reduce the chance of cold rolled coil produces dark spots.

5, the annealing process, the rational blowing hydrogen technology can reduce CRC spots defects.

6, the strip surface plasma treatment when residual chlorine rinse is not clean, chlorine ions remaining in the strip surface, electrochemical corrosion occurs, it generates black Fe3O4.

Control measures:

1, to improve chilled coil-shaped plate-shaped, according to the impact on the quality of the strip surface after annealing, annealing the substrate should be used for micro-edge rolling waves rolling.

2, optimization of the work roll roughness which is 0.8-1.0μm ideal.

3, optimized rolling finished coiling tension winding tension in the range 20-40Mpa more appropriate.

4, a suitable emulsion of the emulsion should be appropriate to reduce the concentration of the emulsion, and to avoid mixing of low chain hydrocarbon oils in the rolling oil in order to improve volatility. Quaker N680-2DPD emulsion better.

5. adjust the mill emulsion purge purge system pressure increases, the gap Anti-wrapped guides gas wall reasonable controls to ensure that gas wall stress, lack of emulsified droplets fall to prevent pressure strip surface.

6, the control of chloride ion concentration should be less than 20mg / L; normal squeezed craft section wringer rolls to avoid the strip surface residual chlorine ions; accelerate the flow of steel coils, steel coils to avoid prolonged stacked to form corrosion, resulting in dark spots.

Post time: Sep-19-2019